Grain and other particulate material falling uncontrolled at high velocities causes: (1) damage to the grain and other particulate material and (2) creates dust. The damage occurs both during fall in a downwardly inclined conduit, as well as upon impact after discharge from the conduit. The damage is apparently caused by particle-to-conduit abrasion and particle-to-particle impact, and these interactions cause fines and dust.
The velocity increase of the material is most rapid in a vertical conduit, but even in a slanting conduit, velocities of several hundred feet per minute are attained in a few feet. A free-falling stream of such material tends to reach a terminal velocity because the air currents within and around the stream cause turbulence when the stream is unconfined. Upon discharge, grain or other particulate material flowing in conduits can reach velocities well above such terminal velocities. In a long conduit, the velocity of the stream can exceed even two thousand feet per minute. It is believed that the damaging velocity is not highly dependent on the angulation of the conduit. As such, the damaging velocity is roughly the same for a given stream whether it is falling in a vertical conduit or an angled conduit.
For a given type of grain or other particulate material, a velocity of 1600 feet per minute is the approximate damaging velocity in many cases. Damage to the material and creation of dust as the result of high conduit velocities also occurs with materials other than grain, although it is most important in respect to grain because of the relative frangibility and layered structure of grain kernels.
To prevent a falling particulate stream of material from exceeding damaging velocity and generating excessive dust, one straightforward approach is to limit the distance of the drop or to angulate the conduit so that the velocity increase is diminished. However, it is difficult to avoid a substantial elevation change in many instances, as for example in loading grain or other particulate material into the hold of a ship.
A flow restriction in the path of the falling material may slow the material velocity. This is often achieved by devices called “dead boxes” which have a narrow fixed throat section mounted directly in the conduit. However, dead boxes are effective primarily in those situations where the grain or other particulate material flow rate (i.e., bushels per hour) is constant or within a relatively narrow range so as to avoid “surges.” However, constant velocity is not usually the case. In the typical situation, surges, abrupt changes in flow rate, occur repeatedly. Surging occurs, for example, when a conveyor bucket empties into the upper end of the chute and a period of lower flow may follow, until another bucket refills the chute. Non-uniform moisture content in the grain or other particulate material is another cause of surges.
When the flow rate is uneven, the use of a fixed restriction such as a dead box to retard flow is of little effect. In periods of low flow rate, the small stream passes almost unrestrained through the throat opening, but at periods of heavy flow, a “head” of grain or other particulate material builds up rapidly above the throat. This can cause bridging or clogging which can choke off flow completely.
In addition to the problem of damage to the grain or particulate material due to high falling velocities, air entrained within the falling stream is a significant problem due to the creation of dust. Ambient dust as a result of a falling stream of particulate material typically requires workers to wear masks or other protective gear. Furthermore, the work environment is clouded by the dust and workers have difficulty seeing for secure footing and evaluation of the level of fill of the vessel receiving the grain or particulate material.
Known methods and apparatus attempting to reduce the dust and fall velocity of grain or other particulate material in vertical conduits by which the velocity can be prevented from exceeding the damaging value even under widely varying flow rates are disclosed in U.S. Pat. Nos. 6,085,987 and 4,342,383, each of which is hereby incorporated by reference in its entirety.
The devices in each of these cited patents include an array of downwardly and inwardly sloping blades supported by the body of an accumulator. The blades have lower ends which define an opening between them, the opening having an area that at its maximum is substantially smaller than the area of the conduit. The overlapping blades are angled inwardly so that they deflect the grain particles centrally as they fall. The inward deflection of the particles toward the smaller area of the throat causes a mass of grain or other particulate material particles to accumulate above the blades and over the opening in an accumulation chamber within the conduit.
Variable biasing means act on the blades to urge them inwardly and the biasing means is responsive to the weight of the accumulated mass of the particles to provide a larger opening as the weight increases, thereby releasing particles more rapidly from the accumulation space above the blades and reducing the area of the opening as the weight of particles decreases.
However, the adjustability of the biasing mechanism disclosed in these patents in some instances is inadequate. In an accumulator or regulating device, it is important to keep the biasing force of the blades on the grain or other particulate material flow without applying excessive force to cause the grain or other particulate material to back-up and the accumulation mass above the gate or opening of the blades to grow too large and become clogged or jammed.
As such, there is a need for an improved system for regulating the flow of grain or other particulate material that overcomes these and other problems in the art, particularly the excessive generation of dust and damage to the falling grain or other material without creating a blockage of accumulated grain.